1. Field of the Invention:
The present invention relates to an optical method for determining the average radius and/or the average length of particles, such as fibers, carried by a flowing medium.
2. Prior Art:
There are instruments which are used as particle content meters. In U.S. Pat. No. 4,110,044 such an instrument is described which includes a measuring head, by which particle content in a flowing medium is indicated. In U.S. Pat. No. 4,318,180 an instrument is disclosed having three measuring heads having mutually different resolutions which are used to measure the particle size distribution of particles in a flowing medium. These instruments are used to make measurements on fiber suspensions, and in particular on such suspensions which are used as basic material for paper manufacture.
Normally, the fibers in such a fiber suspension have a fairly predetermined relation between their thickness and their length. The results from the measurements in accordance with the teachings of U.S. Pat. No. 4,318,180 on the fiber suspensions are based on this relationship.
However, in order to provide different paper qualities the fibers in the fiber suspensions are sometimes preprocessed in some way. For instance they may pass through grinding operations. By these grinding operations the fibers are squeezed and twisted into bands and after this treatment the fiber radius and the fiber length have no longer a predetermined relationship to each other. It has become apparent that information especially about the average radius, but also about the average length of the fibers after grinding, gives a principal indication of the effectiveness of the grinding device.